It has been known that activated carbon, which is a porous carbon, may be fabricated by a method in which a source material is heated and carbonized under a non-oxidizing atmosphere. Examples of the source material include: plant-originating source materials such as lignin, cellulosic substances including wool pulp, saw dust, coconut husk, cottonseed hull, and chaff, starchy substances including foxtail millet, Japanese barnyard millet, and corn; mineral-originating source materials such as coal, tar, and petroleum pitch; and synthetic resins such as phenolic resin and polyacrylonitrile. The techniques for treating the carbonized substances of these source materials with a chemical agent to activate the carbonized substances are also well known.
Recently, it has been confirmed that activated carbon having a specific surface area as high as 3000 m2/g can be obtained by using potassium hydroxide as an activator agent, mixing an organic resin with the activator agent, and heating it under a non-oxidizing atmosphere, which has drawn attention (see Patent Document 1).
However, for commercial use on an industrial scale, this method still has many problems as follows. For example, it requires an activator agent in an amount more than four times the amount of the organic resin. For that reason, the recovery and recycling of potassium is attempted, but the recovery rate is low, increasing the cost. Moreover, alkali metal evaporates during the heating process for the activation, contaminating or damaging the heating furnace, and it also can be a cause of erosion when used for various industrial materials. Furthermore, activated carbon treated with an alkali metal compound is highly flammable and therefore easily catches fire.
In view of such problems, the following proposals have been made.
(1) A method of fabricating activated carbon that includes a step of mixing an organic resin with at least one alkaline-earth metal compound selected from an oxide, a hydroxide, a carbonate, and an organic salt of an alkaline-earth metal, and sintering the mixture in a non-oxidizing atmosphere (see Patent Document 2).
(2) A method of fabricating activated carbon, characterized by using an organic acid-magnesium salts (for example, magnesium citrate) having 6 or more carbon atoms in the structural formula as the source material, heating the organic acid-magnesium salts to 300° C. or higher under an inert atmosphere, and thereafter cooling and acid-washing it (see Patent Document 3).